1. Field of the Invention
The present invention relates to a machine for processing metal in sheet or plate form, especially for bending metal sheets, with a lower bending tool and an upper bending tool, these two tools cooperating to perform the bending of the metal sheet, and with a work table, whereby one of the bending tools is supported by an elastic supporting member or by a oil cushion, to provide a direct or indirect elastic supporting.
2. Description of the Prior Art
A frequent occurrence in high-pressure press brakes is that while a work-piece is being dealt with, the push-rod bends up and the work-table bends down, with the result that there remains between the upper tool mounted on the push-rod and the lower tool monted on the work table a gap which is larger towards the centre than at both ends; machining accuracy is therefore impaired. It is therefore necessary to avoid such a deformation of the upper and/or lower tool, or to compensate for such a deformation. For the solution of this problem, it has been proposed to use Hanni et al, U.S. Pat. Nos. 3,682,465 and 3,829,074 a work-table for machines for processing metal in sheet or plate form, more particularly press brakes, which compensate automatically for a deformation of this kind or ensures that no such deformation can occur. This is achieved by providing the work-table with a work-table panel, a support element therefor extending the length of the work-table panel and mounted in a member for vertical displacement therein and defining therewith a chamber for receiving oil on which the support element will rest. According to an especially favourable form of execution of such a work-table, there is provided an elastic diaphragm which covers the oil-receiving chamber and on which the support element will rest. In this way, all sealing problems are overcome and such a machine will be less expensive in construction and more reliable in use.
Such a work-table has proved very reliable and it has been shown that very precise work can be performed with a machine equipped with such a work-table. However, it had to be recognized as disadvantageous that the machining accuracy is impaired as soon as the work-piece is much shorter than the work-table. If only a part of the work table is subjected to high pressure during the bending step, the work-piece may be pressed too much at its ends, resulting in an unprecise machining there.